No objections to figma, as I don’t think there is a proper open source alternative? What about the one that @loic mentioned in Penpot | Design Freedom for Teams - it doesn’t have the necessary features? I would prefer to avoid proprietary tools as much as possible, especially for things that involve communication and is used by us to produce open source. However, I know that’s not always possible or practical - I’d just like to make sure we checked, and that there is a good reason to balance that choice.
If we go for a proprietary SaaS product, +1 to your concerns @Fox, we need to make sure that the designs keep being exported and available in a public repository with an open source license. SaaS providers have an incentive to try to keep the data as much as possible on their side, and make it hard to migrate out. If it were to become inaccessible (eg account blocked), we need to ensure we always have a backup on our side.